Our long-term goal is to understand how ecdysteroids and juvenile hormone (JH) act to coordinate insect growth and development. Ecdysteroids cause molting, both suppressing on-going intermolt gene expression and activating the cascade of genes necessary for the molt. Moreover, ecdysteroids are important for maintenance of tissue synchrony during the molt. JH determines whether the molt will be progressive or not; in its presence metamorphosis cannot occur. Thus, JH prevents ecdysteroid's activation of previously unexpressed genes that allow the cell to change its differentiated state. Our model for studying this action is the insect epidermis which makes the cuticle, i.e. the exoskeleton, and which is a single cell layer thick and can readily be cultured. Our specific aims for the next 5 years are: 1) To characterize the regulatory regions of the several larval cuticular genes and dopa decarboxylase and to study their possible interactions with ecdysteroid and JH receptors and/or the transcription factors that these hormones induce. 2) To clone, characterize, and study the hormonal control of a pupal-specific cuticle gene to complete our arsenal of epidermal genes that are hormonally regulated at metamorphosis. 3) To determine the role in molting and metamorphosis of the ecdysteroid-induced transcription factor ("RAR") that shows significant similarity to the mammalian retinoic acid receptor. 4) To examine possible changes in EcR subtypes in the epidermis through larval molting and metamorphosis by in situ hybridization and immunocytochemistry and how they are regulated by the hormonal milieu. These studies will allow us to define at the molecular level how ecdysteroids and JH regulate insect growth, molting, and metamorphosis. This information can lead to design of new types of insect growth regulators essential to the control of disease vectors. Also, emerging similarities between the actions of JH and of retinoic acid in the regulation of cell differentiation, particularly in mammalian epidermis, make the insect epidermis a possible nonvertebrate model for study of common mechanisms involved.